Obesity is epidemic in the US and worldwide. Body weight is normally regulated by an endocrine feedback loop, where the hormones insulin and leptin are secreted into the bloodstream in direct proportion to body fat stores. These circulating hormones then interact with a key subset of neurons found in the hypothalamic arcuate nucleus of the brain to regulate a number of physiological processes, including food intake and energy expenditure, that ultimately function to maintain body weight within a normal range. Obesity, which is commonly accompanied by diabetes, is characterized by hypothalamic resistance to the normal effects of these hormones, i.e. food intake and body weight remain elevated despite increased levels of insulin and leptin. In order to adequately treat obesity, we first need to understand the mechanisms causing leptin resistance. Yet we currently do not have a good understanding of the normal signaling mechanisms that insulin and leptin use to activate arcuate nucleus neurons. Initial studies carried out by the applicant demonstrated that signaling through the intracellular signal transduction enzyme, phosphatidylinositol 3-kinase, in arcuate nucleus neurons is required for the food intake lowering effects of leptin and that insulin also activates this signaling pathway in these neurons. The aims of the proposed studies are to identify the specific phenotype of neurons in which PI3K signaling is required, to determine if impaired signaling through PI3K accounts for hypothalamic leptin and insulin resistance as it does peripheral insulin resistance in the setting of diabetes, and finally to determine if a gene therapy approach to increase PI3K signaling in arcuate neurons can attenuate or prevent diet-induced obesity. The overarching goals of the proposal are to improve our understanding of the basic mechanisms, both cellular and neuroanatomical, by which insulin and leptin regulate the function of key neurons found in the hypothalamic arcuate nucleus. This information will then be applied to the problem of diet-indcued obesity and resistance to the normal effects of these hormones. It is hoped that these studies will provide attractive molecular targets for drug development. These aims also provide the background and training necessary for the development of an independent research program and will be conducted in the context of rich training environment